This invention relates to an optical fiber mechanism and connector assembly employing same for performing connection with precise positioning of fiber optic cables and the optical fiber thereof. More specifically, this invention relates to such a connector for use with both single and multimode fibers, but the preferred embodiment finds special use with single mode fiber optic cables.
The use of optical fibers as a means for transmitting optical signals in the field of optical communications has been known for many years. When employed in such systems, it is necessary to interconnect different fibers within the system to complete the communications link. However, in such connections it is often found that not only are there transmission losses when the light is transmitted through the optical fibers, but extensive transmission losses also result from the actual fiber interconnections themselves.
In order to eliminate or minimize such interconnection losses, fiber alignment must be achieved with accuracy on the order of microns, and at the same time the fibers have to closely abut in a manner such as to not damage the cleaved or polished fiber ends. More particularly, in the prior art in connecting the fiber ends, a rotating movement often occurs and the ends of the fibers become damaged or scarred thereby, resulting in additional transmission losses. Moreover, although the fiber ends will initially be in abutment upon initial connection, due to temperature changes, the body holding the fibers expand or contract ultimately resulting in a gap between fiber ends and consequently, additional interference losses.
One prior art approach to centering the fibers or waveguides within aligned connectors is disclosed in U.S. Pat. No. 4,440,469 to Shoemaker. The device of Shoemaker is an SMA-style optical waveguide connector, the type to which this invention is directed, and includes a tubular contact body having an axial passageway profiled for receiving a primary ferrule therein. The passageway is further profiled for retaining the primary ferrule at a rearward location, which ferrule receives an optical waveguide therethrough with a forward end segment of the waveguide extending forward from a forward end of the contact body. An alignment ferrule is provided and is mounted over the forward end of the contact body and received on a forward segment of the optical waveguide. The forward end of the primary ferrule and the inner profile of the contact body passageway are structured to interfit and define a region wherein adhesive material is inserted from the forward terminal end of the connector assembly. The adhesive is retained within this region by the alignment ferrule which fits over the forward segment of the optical waveguide.
Although initially aligning the fiber very precisely, as the adhesive sets, some shrinkage of the adhesive occurs in the device of Shoemaker, and it is not possible to achieve fine fiber alignment readily and reliably with such an arrangement. Moreover, the use of the adhesive complicates the assembly operation and requires long setting times and often, due to the setting of the adhesive, as noted above, even if misalignment does not occur, changes in temperature will cause shrinkage or expansion of the adhesive ultimately resulting in creation of a gap and in the fiber ends being moved out of abutment with each other.
An alternative approach to solving these problems is disclosed in U.S. Pat. No. 4,487,474 which teaches the use of a pair of ceramic optical plugs having optical fibers extending coaxially therethrough which fit within a ceramic sleeve. A coupling nut is used to hold the two plugs together to effect the interconnection between the optical fibers.
Although generally providing improved results over the adhesive employing prior art systems, the connector employing the ceramic plug as disclosed in this patent includes disadvantages in that it is difficult to ensure that the two ceramic plugs are tightly held against each other, and further, there is the possibility that rotation of the plugs and fibers with respect to each other will result in scarring of the fiber faces upon repeated connection and disassembly of the connector device. As previously noted, such scarring can cause significant transmission losses at the interface. Further, as noted previously, although it is possible to maintain the plugs in abutment, it is often the case that the plug will shrink or expand due to temperature changes, which results in an interference causing gap between the fiber ends.
In another known prior art device the plugs are used with adhesive to ensure that the fiber ends remain flush with the plugs. However, this type of system requires polishing and buffing of the ends of the fibers. This buffing will often result in the end faces becoming concave in the direction of its respective holding plug. Thus, in assembling the two plugs against each other a gap will result between the concave end surfaces with all the attendant disadvantages discussed above.
The above-discussed gaps between fiber ends, while causing interference, are not as disruptive in the case when multimode fiber optic cables are used. However, in the case of single mode fiber optic cables, the resultant gap can cause unacceptable transmission losses. In the prior art there are only several ways to reduce these losses in the case of single mode fiber optic cables.
One solution provided is to epoxy the fibers in place, but this includes all the disadvantages discussed above. A second approach is to use an arrangement of several ferrules concentrically assembled in what is known as "stratus" configuration. However, this arrangement is still prone to gap creation and is generally not satisfactory. Moreover, this arrangement is also very complicated to assemble. A third arrangement, which is more satisfactory in terms of results, is a technique of molding the fiber into a molded connector.
Such molded connectors or methods of molding connectors are disclosed in U.S. Pat. Nos. 4,107,242; 4,213,932; 4,264,128; and 4,512,630. Although providing improved results, these devices are complicated to assemble requiring complicated molding devices. As a result expenses are increased. Moreover, the devices are not field terminable.
As can be seen, the prior art systems suffer from a number of disadvantages at the fiber connection ends. Further, the connectors themselves do not provide a simple and secure method of attaching the fiber optic cables to the connector assembly itself. Generally, some type of simple crimping arrangement is employed resulting in a danger of the internal waveguide or core fiber of the fiber optic cable being deformed or damaged as a result of the crimping operation. In addition, simple crimping from the outside of the cable is often not satisfactory in terms of holding efficiency since the fiber waveguide will be able to slide longitudinally relative to the outer layers of the cable.